Additive for, treatment fluid for, and method of plugging a tubing/casing annulus in a well bore

ABSTRACT

For tubing/casing annulus plug treatment to plug a well, a tubing/casing annulus plug additive including a dry mixture of water soluble crosslinkable polymer, a crosslinking agent, a filter aid, and an optional reinforcing material, preferably of fibers and/or comminuted plant materials. The method of forming a tubing/casing annulus plug fluid includes contacting the additive with water or an aqueous solution, with a method of plugging the tubing/casing annulus of a well further including the step of injecting the fluid into the annulus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to tubing/casing annulus plug additivesand to methods of making such additives, to tubing/casing annulus plugtreatment fluids made therefrom and to methods of making such fluids, tomethods of modifying a well fluid using such additives and/or fluids, tomethods of operating a well using such additives and/or fluids, and tomethods of plugging a tubing/casing annulus in a well bore. In anotheraspect, the present invention relates to tubing/casing annulus plugadditives comprising polymer, crosslinking agent, filter aid, andoptionally reinforcing materials and to methods of making suchadditives, to tubing/casing annulus plug treatment fluids made therefromand to methods of making such fluids, to methods of modifying a wellfluid using such additives and/or fluids, to methods of operating a wellusing such additives and/or fluids, and to methods of plugging atubing/casing annulus in a well bore. In another aspect, the presentinvention relates to tubing/casing annulus plug additives comprising adry mixture of polymer, crosslinking agent, filter aid, and optionallyreinforcing materials and to methods of making such additives, totubing/casing annulus plug treatment fluids made therefrom and tomethods of making such fluids, to methods of modifying a well fluidusing such additives and/or fluids, to methods of operating a well usingsuch additives and/or fluids, and to methods of plugging a tubing/casingannulus in a well bore. In even another aspect, the present inventionrelates to additives comprising polymer and diatomaceous earth (“DE”)and to methods of making such additives, to tubing/casing annulus plugtreatment fluids made therefrom and to methods of making such fluids, tomethods of modifying a well fluid using such additives and/or fluids, tomethods of operating a well using such additives and/or fluids, and tomethods of plugging a tubing/casing annulus in a well bore.

2. Description of the Related Art

Portland cement is commonly used in oil field applications such as oilwell cement jobs. Portland cements can be tailor-made for the specificconditions of each well. A description of the state of the art in oilwell cementing technology is given in Basic Cementing, PetroleumPublishing Co., 1977 (reprinted from a series of articles appearing inthe Oil and Gas Journal) and Rike, J. L., et al, Squeeze Cementing:State of The Art, Journal of Petroleum Technology, (January 1982), pp.37-45.

Formulation of the cement in the field is largely a product of trial anderror by field personnel to meet irregularities in the cementingcomposition and the downhole environment. Cement quality control isdifficult to achieve under such conditions. As a result, Portland cementcan exhibit premature set-up, cracking, or shrinking upon curing. Thisfeature of Portland cement limits its usefulness in wellbore treatmentsto repair leaks in wellbore casing or tubing by plugging thetubing/casing pair annulus. Use of other available methods to remedyleaking wellbore tubulars, including workovers and redrilling, can beextremely cumbersome and expensive.

U.S. Pat. No. 4,730,674, issued Mar. 15, 1988 to Burdge et al., notedthat a wellbore treatment process was needed for preventing or repairingleaking tubulars which was both economically and operationallyattractive. Burdge et al. further noted that a process was needed whicheffectively employed a plugging material having a broad range of highlycontrollable and predictable set-up times for ease of operation anddesign. Burdge et al. even further noted that a process was needed whichemployed a plugging material which was not as susceptible as Portlandcement to shrinking and cracking when applied to a tubing/casing annulusin a wellbore.

In an effort to overcome the deficiencies of the prior art and tofulfill the perceived needs, U.S. Pat. No. 4,730,674 discloses the useof a water soluble carboxylate crosslinking polymer along with a chromiccarboxylate complex crosslinking agent in the plugging of atubing/casing annulus in a wellbore, and at column 2, lines 30-35,specifically teaches away from the use of solids in the plugging fluidinjected into the wellbore.

Thus, while U.S. Pat. No. 5,377,760, issued Jan. 3, 1995 to Merrilldiscloses addition of fibers to an aqueous solution of partiallyhydrolyzed polyacrylamide polymer, with subsequent injection into thesubterranean to improve conformance, the performance requirements ofconformance improvement treatment polymers are so different from thoseof polymers for plugging an abandoned well, that such would notnecessarily work for plugging tubing/casing annulus. Furthermore, Burdgeet al. teach away from injection a solid containing polymer into thewellbore to plug a tubing/casing annulus.

Additionally, Merrill's conformance treatment method of mixing thefibers with the polymer solution followed by injection, requires amultiplicity of storage and mixing tanks, and a metering system whichmust be operated during the operation of the well. Specifically, a firsttank will store a water and polymer solution, a second tank will store awater and cross-linking solution, and a third tank will be used to mixfibers with polymer solution from the first tank to create apolymer/fiber slurry. This polymer/fiber slurry is then metered from thethird tank and combined with crosslinking solution metered from thesecond tank to the well bore.

As an advance over the above prior art, U.S. Pat. No. 6,218,343, issuedApr. 17, 2001, to Boyce D. Burts, Jr., for “Additive for, treatmentfluid for, and method of plugging a tubing/casing annulus in a wellbore,” discloses an additive including a dry mixture of water solublecrosslinkable polymer, a crosslinking agent, and a reinforcing materialof fibers and/or comminuted plant materials. The method of forming afluid includes contacting the additive with water or an aqueoussolution, with a method of treating the formation further including thestep of injecting the fluid into the formation.

While not believed to be related prior art because they relate todifferent types of well operations, for completeness, attention isdirected to five other similar “dry mixture” patents by Boyce D. Burts,Jr., which were filed on the same day (Oct. 31, 1997) as the '343Patent: U.S. Pat. No. 6,102,121, issued Aug. 15, 2000, for “Conformanceimprovement additive, conformance treatment fluid made therefrom, methodof improving conformance in a subterranean formation,” U.S. Pat. No.6,098,712, issued Aug. 8, 2000, for “Method of plugging a well,” U.S.Pat. No. 6,016,879, issued Jan. 25, 2000, for “Lost circulationadditive, lost circulation treatment fluid made therefrom, and method ofminimizing lost circulation in a subterranean formation,” U.S. Pat. No.6,016,871, issued Jan. 25, 2000, for “Hydraulic fracturing additive,hydraulic fracturing treatment fluid made therefrom, and method ofhydraulically fracturing a subterranean formation,” and U.S. Pat. No.6,016,869, issued Jan. 25, 2000, for “Well kill additive, well killtreatment fluid made therefrom, and method of killing a well.”

A number of patents discuss the use of diatomaceous earth (“DE”) in awell operation.

U.S. Pat. No. 3,380,542, issued Apr. 30, 1968 to Clear, for restoringlost circulation discloses a oil-based drilling fluid, containing aslurry of diatomite and asbestos, used to restore lost circulationduring well drilling operations.

U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, discloses thatvarious formation sealing agents have been used in the art to formformation seals and/or filter cakes on the wall of a well bore,including diatomaceous earth.

U.S. Pat. No. 4,110,225, issued Aug. 29, 1978 to Cagle, discloses thatzones of lost circulation and other undesired fluid communicationchannels into a wellbore are sealed by isolating a volume in the wellincluding such a zone and applying greater than formation pressure to anovel slurry spotted in the zone until it hardens into a solid,drillable seal. The slurry contains per barrel from 5-50 poundsdiatomaceous mix, from about 35 to about 350 pounds of oil well cement,and at a minimum about 5 to 6 pounds of a flake type lost-circulationagent. This '225 patent cites a number of patents that disclosecement/diatomaceous earth compositions, including U.S. Pat. Nos.2,585,336; 2,793,957; 2,961,044; 3,467,198; and 3,558,335.

Regarding these patents, the '225 patent notes the following:

-   -   Regarding U.S. Pat. No. 2,585,336, the '225 patent notes, “a        mixture is made using from 2% to 100% diatomaceous earth,        compared to the content of the cement in the slurry. The aim of        the inventors was to prevent perlite from settling and to        produce a lightweight cement. The diatomaceous earth-cement        described in the disclosure is a mixture of Portland cement,        perlite and diatomaceous earth, lime, and asbestos fibers.”    -   Regarding U.S. Pat. No. 2,793,957, the '225 patent notes,        “refers to a highly permeable cement formed by use of the same        basic mixtures of diatomaceous earth with Portland cement, the        diatomaceous earth present being from five to seven times the        proportion of the Portland cement in the slurry. The aim of the        inventors was to produce a light highly permeable cement,        entirely opposite to the purpose of my invention.”    -   Regarding U.S. Pat. No. 2,961,044, the '225 patent notes,        “discusses and claims a cement composition which has        diatomaceous earth in the amounts of from 30% to 70% of the        Portland cement. The reason for using the diatomaceous earth was        to prevent the strength retrogression of a salt-saturated        cement. Thus, while Shell wishes (among other uses) to employ        his mixture for squeeze cementing, he produces a relatively        high-strength cement plug. There is a real tendency when        redrilling such a plug for the bit to be deflected or        sidetracked so that the new hole is beside rather than through        the bore and the seal is ineffective. This is completely        different from my invention which minimizes such tendency by        producing a plug at least as drillable as the formation in which        it is set. Also, Shell is directed to operations using        salt-saturated cement slurries, while I prefer using a fresh or        brackish water slurry. I employ lost-circulation agents; he        makes no teaching of using such additives. Accordingly, his        teaching is quite far from mine.”    -   Regarding both U.S. Pat. Nos. 3,467,198 and 3,558,335, the '225        patent notes, “describe cement compositions having diatomaceous        mix present in the amounts from 0.5% to 10% of the amount of        Portland cement present to prevent solids-settling.”

U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, disclosesslurries to seal permeable earth formations encountered in the drillingof wells, comprising finely divided paper, diatomaceous earth, and in afurther embodiment, lime. A slug of the slurry is spotted at the locusof the permeable formation and defluidized to form a formation seal onwhich a mud sheath is then deposited.

U.S. Pat. No. 4,505,751, issued Mar. 19, 1985, discloses asilicate/silica cement in oil field applications, including diatomaceousearth as a species of silica compound.

While not believed to be analogous prior art because it relates toearthen pits (for example a ditch) and not to subterrean wellbores norwell operations, U.S. Pat. No. 5,947,644, issued Sep. 7, 1999 to Gibbonset al., is included herein for completeness because it discloses agelable slurry of aqueous solvent, a crosslinkable polymer, acrosslinking agent, and unconsolidated solids such as diatomaceousearth. This gelable slurry is placed in an earthen pit and allowed toform into a fluid impermeable barrier wall in the earthen pit. Thepolymer serves to bind the unconsolidated solids to convert the gelableslurry to a non-deformable gelled continuum of consolidated solids,which forms the barrier wall in the earthen pit. As disclosed in the'644 patent in the Summary of the Invention section, at col. 1, lines57-67, this gelable slurry is prepared by first forming a liquidgelation solution of the polymer and crosslinking agent, to which issubsequently mixed with the unconsolidated solids, or alternatively, bysequentially mixing the aqueous solvent, crosslinkable polymer, andpolymer crosslinking agent with the unconsolidated solids.

Thus, in spite of the advancements in the prior art, there still needfor further innovation in the tubing/casing annulus plug additives.

There is need for further innovation for tubing/casing annulus plugadditives utilizing a water soluble polymer.

There is another need for a tubing/casing annulus plug additive whichwould allow for simplification of the mixing equipment.

These and other needs in the art will become apparent to those of skillin the art upon review of this specification, including its drawings andclaims.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide for furtherinnovation in tubing/casing annulus plug additives.

It is an another object of the present invention to provide for furtherinnovation for tubing/casing annulus plug additives utilizing a watersoluble polymer.

It is even another object of the present invention to provide for atubing/casing annulus plug additive which would allow for simplificationof the mixing equipment.

These and other objects of the present invention will become apparent tothose of skill in the art upon review of this specification, includingits drawings and claims.

According to one embodiment of the present invention, there is provideda tubing/casing annulus plug additive comprising a dry mixture of watersoluble crosslinkable polymer, a crosslinking agent, and a filter aid.

According to another embodiment of the present invention, there isprovided a well fluid comprising a tubing/casing annulus plug fluid,water soluble crosslinkable polymer, a crosslinking agent, and a filteraid.

According to even another embodiment of the present invention, there isprovided a method of modifying a tubing/casing annulus plug fluid. Themethod includes contacting the tubing/casing annulus plug fluid with awater soluble crosslinkable polymer, crosslinking agent, and filter aidto form a modified tubing/casing annulus plug fluid.

According to still another embodiment of the present invention, there isprovided a method for plugging a tubing/casing annulus formed between acasing and a tube internal to the casing in a wellbore in fluidcommunication with a subterranean hydrocarbon-bearing formation. Themethod includes providing a tubing/casing annulus plug fluid comprisingwater soluble crosslinkable polymer, a crosslinking agent, and a filteraid. The method also includes injecting the tubing/casing annulus plugfluid into the annulus. The method also includes dewatering the fluid toform a filter aid plug, and to form a dewatered fluid which subsequentlycrosslinks to substantial completion in said annulus to substantiallyplug said annulus.

According to yet another embodiment of the present invention, there isprovided a method for plugging a tubing/casing annulus formed between acasing and a tube internal to the casing in a wellbore in fluidcommunication with a subterranean hydrocarbon-bearing formation. Themethod includes providing a tubing/casing annulus plug fluid comprisingwater soluble crosslinkable polymer, a crosslinking agent, and filteraid. The method includes injecting the tubing/casing annulus plug fluidinto the annulus. The method includes applying pressure to dewater thefluid to form a filter aid plug, and to form a dewatered fluid whichsubsequently crosslinks to substantial completion in said annulus tosubstantially plug said annulus.

According to even still another embodiment of the present invention,there is provided a method of circulating a tubing/casing annulus plugfluid in a welbore penetrating a subterranean formation. The methodincludes providing a tubing/casing annulus plug fluid comprising wateror an aqueous solution, water soluble crosslinkable polymer, acrosslinking agent, and a filter aid. The method includes circulatingthe tubing/casing annulus plug fluid in the wellbore.

According to even yet another embodiment of the present invention, thereis provided a method of modifying a tubing/casing annulus plug fluidcirculating in a wellbore penetrating a subterranean formation. Themethod includes introducing a water soluble crosslinkable polymer,crosslinking agent, and filter aid to the circulating tubing/casingannulus plug fluid.

Various further embodiments of any or all of the above embodimentsinclude any or all of the following in any combination: the filter aidis selected from the group consisting of diatomaceous earth, perlite,glass beads, magnesium silicate, solid thermoplastic or thermosetpolymer beads, talc, and calcium silicate; or the polymer is an acarboxylate-containing polymer, and the crosslinking agent is selectedfrom the group consisting of chromium (III) carboxylate complexes,aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates,titanium chelates, phenols, substituted phenols, ethers, aluminumcitrate, and aluminates; the filter aid comprises at least one ofdiatomaceous earth or pearlite; the polymer comprises a low molecularweight polymer having a molecular weight less than 500,000, and a highmolecular weight polymer having a molecular weight of at least 500,000;the polymer is a water soluble, carboxylate containing acrylamide, andthe crosslinking agent is a chromium (III) carboxylate complex; thefilter aid is diatomaceous earth; the filter aid is pearlite; thereinforcing material selected from the group consisting of hydrophilicfibers, hydrophobic fibers, and comminuted plant material; and/orvarious weight percentages are in the range of about 4 to about 35weight percent polymer, in the range of about 1 to about 10 weightpercent cross linking agent, and in the range of about 55 to about 95weight percent filter aid, based on the total weight of the polymer,cross linking agent and filter aid.

These and other embodiments of the present invention will becomeapparent to those of skill in the art upon review of this specificationand claims.

DETAILED DESCRIPTION OF THE INVENTION

The tubing/casing annulus plug additive of the present inventionincludes polymer, cross-linking agent, filter aid, and optionallyreinforcing materials, preferably for example either fibers orcomminuted particles of plant materials, and optionally any othermaterials that are known in the art. In a preferred embodiment of thepresent invention, the tubing/casing annulus plug additive is a drymixture of polymer, crosslinking agent, and filter aid, and optionallyreinforcing materials.

The present invention provides a wellbore treatment additive, fluid andprocess for plugging a tubing/casing annulus in a wellbore incommunication with a subterranean hydrocarbon-bearing formation. Theprocess is particularly applicable to injection or production wells inoil fields wherein the tubing and/or casing have developed leaks whichenable undesirable flow of fluids into, out of, or vertically throughthe annulus formed between the tubing/casing pair. Leaks in the tubingand/or casing can be caused inter alia by corrosion, mechanical abrasionor thread leaks.

The leaks can result in serious operational, safety and/or environmentalproblems, especially where brines leak into and fill the annulus betweenthe tubing/casing pair. The brines cause severe corrosion of the metalmaterials in the wellbore which ultimately can lead to loss of the well.

The present invention prevents the unwanted vertical flow of fluids inthe tubing/casing annulus as well as unwanted flow of fluids into or outof leaking tubing and/or casing in a cost-effective and operationallyattractive manner. The process is applicable as a remedial treatment forexisting leaking wells and as a preventive treatment for new ornon-leaking wells.

The objectives of the present invention are achieved by means of aplugging material comprising a tailor-made crosslinked polymer gel.

“Gel” as used herein is directed to a continuous three-dimensionalcrosslinked polymeric network having an ultra high molecular weight. Thegel contains a liquid medium such as water which is confined within thesolid polymeric network. The fusion of a liquid and a solid componentinto a single-phase system provides the gel with a unique phasebehavior. Gels employed by the present invention have sufficientstructure so as not to propagate from the confines of a plugged volumeinto a less permeable region of the formation adjoining the volume wheninjected into the volume.

“Plugging” is a substantial reduction in permeability of a volume in thewellbore sufficient to prevent or inhibit fluid flow therethrough.

“Partially gelled” solutions are also referred to herein. A partiallygelled solution is at least somewhat more viscous than an uncrosslinkedpolymer solution such that it is incapable of entering a less permeableregion where no treatment is desired, but sufficiently fluid such thatit is capable of displacement into a desired treatment zone. Thecrosslinking agent of the partially gelled solution has reactedincompletely with the polymer with the result that neither all of thepolymer nor all of the crosslinking agent in the gelation solution istotally consumed by the crosslinking reaction. The partially gelledsolution is capable of further crosslinking to completion resulting inthe desired gel without the addition of more crosslinking agent.

“Crosslinked to completion” means that the gel composition is incapableof further crosslinking because one or both of the required reactants inthe initial solution are consumed. Further crosslinking is only possibleif either polymer, crosslinking agent, or both are added to the gelcomposition.

The preferred gel of the present invention contains a high molecularweight, water-soluble carboxylate-containing polymer, and a chromiccarboxylate complex crosslinking agent, and optionally reinforcingmaterial such as the preferred fibers and/or comminuted plant material.

The gel is generally prepared by forming in any order, by any suitablemethod and with type of equipment, a uniform gelation solution of thepolymer, crosslinking agent, and fibers and/or comminuted plantmaterial. In a preferred embodiment, the gel is prepared by contacting adry mixture of the polymer, crosslinking agent and fibers and/orcomminuted plant material, with water or an aqueous solution.

Once the solution is formed, the method of the present inventionincludes injecting the solution into the annulus between a tubing/casingpair in a wellbore penetrating a hydrocarbon-bearing formation. Thegelation solution is gelled to substantial completion in the annulusthereby plugging the annulus.

The gelation solution may be advantageously designed to be at leastpartially gelled by the time it reaches the annulus to inhibit orprevent its propagation into a less permeable material, which may adjointhe casing where no plugging is desired, such as a formation matrix. Thegelation solution sets up in the annulus without requiring the furtherinjection of any additional components. The gel is a continuoussingle-phase material which substantially plugs the annulus. After thetreatment, the well may be returned to normal operation.

The process provides distinct advantages over processes known in theart. The gelation solution, as initially injected into the well-bore, isa uniform nonviscous liquid solution prepared at the surface. Theresulting gel forms a tenacious chemical bond with the tubular surfacesand is substantially impermeable to formation fluids. The gel isdesigned to be non-flowing to the maximum rheological stress of thesystem, which enables it to substantially resist displacement from theannulus during oil recovery operations. Yet, the gel is not so strongthat placement of the gel in the annulus precludes subsequent tubepulling or workover operations in the wellbore. The gel is substantiallypermanent and resistant to degradation in the subterranean environment.However, if subsequent removal of the gel from the annulus is desired,it can be dissolved by an external solvent, such as solutions of sodiumhypochlorite, hydrogen peroxide, or any other suitable peroxo compound.

The cementing gel employed in the present invention possesses a broadrange of highly controllable and predictable set-up times and strengths.The process is applicable to a broad range of temperatures, salinities,rock formations, and environments. The practitioner can customize ortailor a gel for specific operational constraints, downholecharacteristics and subsequent performance demands. One can predeterminethe gelation rate and resultant gel strength and stability which arerequired of a gel to meet the performance demands in the wellbore.Thereafter, a cementing gel having the required predetermined propertiesis produced under controlled conditions at the surface by utilizingobserved correlations between specific controllable gelation parametersand resultant gel properties.

A well fluid of the present invention includes well fluid componentsplus the additive of the present invention.

Any suitable relative amounts of the polymer, crosslinking agent, filteraid and the optional reinforcing materials may be utilized in thepresent invention provided that the desired conformance results areachieved. Generally, the relative amounts of each will be determinedbased on the particular application to which the additive is to besubjected. A suitable amount of crosslinking agent is provided to reachthe desired amount of crosslinking. The amount of reinforcing materialis selected to provide desired physical properties.

Any suitable types of filter aid materials as are known in thefiltration art may be utilized as the filter aid component in thepresent invention. All that is necessary is that the filter aid willfunction to be “squeezed” and allow migration of the solution of polymerand crosslinking agent into the formation, and will form a plug of thefilter aid that will hold the solution in place until it sufficientlycrosslinks. Non-limiting examples of which include diatomaceous earth(“DE” or diatomite), perlite (or pearlite), glass beads, magnesiumsilicate, solid thermoplastic or thermoset polymers generally in powderform, talc (naturally occuring form of hydrous magnesium silicatecontaining varying proportions of such associated minerals asalpha-quartz, calcite, chlorite, dolomite, kaolin, magnesite, andphlogopite), and calcium silicate (for example, see, U.S. Pat. No.5,750,038, issued May 12, 1998, to Tsunematsu, for “Method for thepreparation of acid-resistant calcium silicate,” incorporate herein byreference), and any combination of two or more of the above. Preferably,the filter aid is selected from the group consisting of diatomaceousearth perlite (or pearlite), magnesium silicate, and talc. Morepreferably, the filter aid is a mineral based type of filter aid,non-limiting examples of which include diatomaceous earth, pearlite,magnesium silicate, talc and calcium silicate, and any combination oftwo or more of the above. Even more preferably, the filter aid comprisespearlite and/or diatomaceous earth. Still more preferably, the filteraid comprises diatomaceous earth.

The amount of filter aid to be utilized is generally not dependent uponthe amount of polymer or crosslinking agent, but rather, is that amountsufficient to form a plug to retain the polymer in place until itcrosslinks sufficiently to remain in place on its own. However, in aneffort to quantify the amount of filter aid, a weight ratio of filteraid to polymer is provided for convenience.

Generally, the weight ratio of filter aid:polymer in the additive is inthe range of about 100:1 to about 1:100, preferably in the range ofabout 50:1 to about 1:50, more preferably in the range of about 15:1 toabout 1:15, even more preferably in the range of about 5:1 to about 1:5,and still more preferably in the range of about 5:1 to about 1:1.

Commercially, it is envisioned that the additive will be packaged in asingle bag, to promote ease of use and eliminate the necessity of anymeasuring and/or mixing at the well site. As a non-limiting example of acommercial embodiment, a 40 pound bag might contain any where from about1.5 to about 17.5 lbs. polymer, from about 0.4 to about 5 lbs.crosslinking agent, and the balance of from about 17.5 to about 38.1lbs. filter aid.

In weight percentage terms, examples of weight percentage ranges includefrom about 4 to about 35 weight percent polymer, from about 1 to about10 weight percent cross linking agent, and from about 55 to about 95weight percent filter aid, based on the total weight of the polymer,cross linking agent and filter aid. Specific non-limiting examples ofuseful compositions include 4% polymer, 1% cross linker, 95% DE, or 24%polymer, 6% cross linker, 70% DE, or 35% polymer, 10% cross linker, 55%DE.

The particle size distribution of the filter aid is selected to allowdewatering of the filter aid (i.e., the solution containing polymer andcrosslinking agent will separate from the filter aid), and to allowformation of a plug of the filter aid that retains the polymer andcrosslinking agent in the reservoir during crosslinking. It is believedthat the particle size distribution will be determined by the reservoirconditions.

Other additives as are known in the well fluid art may be utilized, nonlimiting examples of which include surfactants, dispersants, retarders,accelerants, weighting agents (such as hematite, barite or calciumcarbonate), lost circulation materials and other additives may beprovided as necessary or desired.

The polymer utilized in the practice of the present invention ispreferably water soluble and must be capable of being pumped as a liquidand subsequently crosslinked in place to form a substantiallynon-flowing crosslinked polymer which has sufficient strength towithstand the pressures exerted on it. Optionally, when reinforcingmaterials are utilized, it would have a network structure capable ofincorporating reinforcing materials.

While any suitable water soluble polymer may be utilized, the preferredpolymer utilized in the practice of the present invention is a watersoluble carboxylate-containing polymer, more preferably a water solublepartially hydrolyzed carboxylate-containing polymer. Thiscarboxylate-containing polymer may be any crosslinkable, high molecularweight, water-soluble, synthetic polymer or biopolymer containing one ormore carboxylate species.

For an example of polymers and crosslinking agents suitable for useherein and details regarding their making and use, please see any of theabove listed patents to Boyce D. Burts, Jr. all herein incorporated byreference, or please see U.S. Pat. Nos. 4,683,949, 4,723,605, 4,744,418,4,770,245, 4,844,168, 4,947,935, 4,957,166 and 4,989,673, 5,377,760,5,415,229, 5,421,411, all herein incorporated by reference.

The average molecular weight of the carboxylate-containing polymerutilized in the practice of the present invention is in the range ofabout 10,000 to about 50,000,000, preferably in the range of about100,000 to about 20,000,000, more preferably in the range of about200,000 to about 15,000,000, and still more preferably in the range ofabout 200,000 to about 10,000,000.

In some instances, a blend of two polymers, a lower molecular weightpolymer and a higher molecular weight polymer may be utilized. Forexample, in some instances where high fluid loss is encountered, such asa hole in the casing, a fault zone, loose sand, unconsolidated zones, orvugular formations, higher molecular weight polymer must be utilized.However, this higher molecular weight polymer causes problems in mixing,pumping and total polymer load. Thus, this higher molecular weightpolymer is mixed with a lower molecular weight polymer to providemixing, pumping and loading as desired.

Generally, this lower molecular weight polymer has a molecular weightless than 1,000,000, preferably less than 500,000, and more preferablyless than 200,000. Generally the lower molecular weight polymer willhave a molecular weight in the range of about 20,000 to less than1,000,000, preferably in the range of about 20,000 to less than 500,000,and more preferably in the range of about 200,000 to less than 500,000.The higher molecular weight polymer generally has a molecular weight ofat least 1,000,000, preferably from about 1,000,000 to about 50,000,000,more preferably from about 5,000,000 to about 20,000,000, and even morepreferably from about 6,000,000 to about 12,000,000.

Biopolymers useful in the present invention include polysaccharides andmodified polysaccharides. Non-limiting examples of biopolymers arexanthan gum, guar gum, carboxymethylcellulose, o-carboxychitosans,hydroxyethylcellulose, hydroxypropylcellulose, and modified starches.Non-limiting examples of useful synthetic polymers include acrylamidepolymers, such as polyacrylamide, partially hydrolyzed polyacrylamideand terpolymers containing acrylamide, acrylate, and a third species. Asdefined herein, polyacrylamide (PA) is an acrylamide polymer havingsubstantially less than 1% of the acrylamide groups in the form ofcarboxylate groups. Partially hydrolyzed polyacrylamide (PHPA) is anacrylamide polymer having at least 1%, but not 100%, of the acrylamidegroups in the form of carboxylate groups. The acrylamide polymer may beprepared according to any conventional method known in the art, butpreferably has the specific properties of acrylamide polymer preparedaccording to the method disclosed by U.S. Pat. No. Re. 32,114 toArgabright et al incorporated herein by reference.

Any crosslinking agent suitable for use with the selected polymer may beutilized in the practice of the present invention. Non limiting examplesof suitable crosslinking agents includes chromium (III) carboxylatecomplexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde,dichromates, titanium chelates, phenols, substituted phenols, ethers,aluminum citrate, and aluminates.

Preferably, the crosslinking agent utilized in the present invention isa chromic carboxylate complex.

The term “complex” is defined herein as an ion or molecule containingtwo or more interassociated ionic, radical or molecular species. Acomplex ion as a whole has a distinct electrical charge while a complexmolecule is electrically neutral. The term “chromic carboxylate complex”encompasses a single complex, mixtures of complexes containing the samecarboxylate species, and mixtures of complexes containing differingcarboxylate species.

The chromic carboxylate complex useful in the practice of the presentinvention includes at least one or more electropositive chromium IIIspecies and one or more electronegative carboxylate species. The complexmay advantageously also contain one or more electronegative hydroxideand/or oxygen species. It is believed that, when two or more chromiumIII species are present in the complex, the oxygen or hydroxide speciesmay help to bridge the chromium III species. Each complex optionallycontains additional species which are not essential to the polymercrosslinking function of the complex. For example, inorganic mono-and/or divalent ions, which function merely to balance the electricalcharge of the complex, or one or more water molecules may be associatedwith each complex. Non-limiting representative formulae of suchcomplexes include:[Cr₃(CH₃CO₂)₆(OH)₂]¹⁺;[Cr₃(CH₃CO₂)₆(OH)₂]NO₃.6H₂O;[Cr₃(CH₃CO₂)₆(OH)₂]³⁺; and[Cr₃(CH₃CO₂)₆(OH)₂](CH₃CO₂)₃.H₂O.

“Trivalent chromium” and “chromic ion” are equivalent terms encompassedby the term “chromium III” species as used herein.

The carboxylate species are advantageously derived from water-solublesalts of carboxylic acids, especially low molecular weight mono-basicacids. Carboxylate species derived from salts of formic, acetic,propionic, and lactic acid, substituted derivatives thereof and mixturesthereof are preferred. The preferred carboxylate species include thefollowing water-soluble species: formate, acetate, propionate, lactate,substituted derivatives thereof, and mixtures thereof. Acetate is themost preferred carboxylate species. Examples of optional inorganic ionsinclude sodium, sulfate, nitrate and chloride ions.

A host of complexes of the type described above and their method ofpreparation are well known in the leather tanning art. These complexesare described in Shuttleworth and Russel, Journal of the Society ofLeather Trades' Chemists, “The Kinetics of Chrome Tannage Part I.,”United Kingdom, 1965, v. 49, p. 133-154; “Part III.,” United Kingdom,1965, v. 49, p. 251-260; “Part IV.,” United Kingdom, 1965, v. 49, p.261-268; and Von Erdman, Das Leder, “Condensation of MononuclearChromium (III) Salts to Polynuclear Compounds,” Eduard Roether Verlag,Darmstadt Germany, 1963, v. 14, p. 249; and incorporated herein byreference. Udy, Marvin J., Chromium. Volume 1: Chemistry of Chromium andits Compounds. Reinhold Publishing Corp., N.Y., 1956, pp. 229-233; andCotton and Wilkinson, Advanced Inorganic Chemistry 3rd Ed., John Wileyand Sons, Inc., N.Y., 1972, pp. 836-839, further describe typicalcomplexes which may be within the scope of the present invention and areincorporated herein by reference. The present invention is not limitedto the specific complexes and mixtures thereof described in thereferences, but may include others satisfying the above-stateddefinition.

Salts of chromium and an inorganic monovalent anion, e.g., CrCl3, mayalso be combined with the crosslinking agent complex to accelerategelation of the polymer solution, as described in U.S. Pat. No.4,723,605 to Sydansk, which is incorporated herein by reference.

The molar ratio of carboxylate species to chromium III in the chromiccarboxylate complexes used in the process of the present invention istypically in the range of 1:1 to 3.9:1. The preferred ratio is range of2:1 to 3.9:1 and the most preferred ratio is 2.5:1 to 3.5:1.

The optional reinforcing material of the present invention may comprisefibers or comminuted particles of plant materials, and preferablycomprises comminuted particles of one or more plant materials.

Fibers suitable for use in the present invention are selected from amonghydrophilic and hydrophobic fibers. Incorporation of hydrophobic fiberswill require use of a suitable wetting agent. Preferably, the fibersutilized in the present invention comprise hydrophilic fibers, mostpreferably both hydrophilic and hydrophobic fibers.

With respect to any particular fiber employed in the practice of thepresent invention, it is believed that the longer the fiber, the moredifficult it is to be mixed uniformly in solution. It is believed thatfibers as long as 12,500 microns may tend to aggregate and form clumps.The shorter the fiber, it is believed the easier it is to mix insolution. On the other hand, the shorter the fiber, the greater thequantity necessary to provide the desired level of strength in areinforced mature gel. In general, the fibers utilized in the presentinvention will have a length in the range of 100 microns to 3200microns, preferable 100 microns to 1000 microns.

Non-limiting examples of suitable hydrophobic fibers include nylon,rayon, hydrocarbon fibers and mixtures thereof.

Non-limiting examples of suitable hydrophilic fibers include glass,cellulose, carbon, silicon, graphite, calcined petroleum coke, cottonfibers, and mixtures thereof.

Non-limiting examples of comminuted particles of plant materialssuitable for use in the present invention include any derived from: nutand seed shells or hulls such as those of peanut, almond, brazil, cocoabean, coconut, cotton, flax, grass, linseed, maize, millet, oat, peach,peanut, rice, rye, soybean, sunflower, walnut, wheat; various portionsof rice including the rice tips, rice straw and rice bran; crude pectatepulp; peat moss fibers; flax; cotton; cotton linters; wool; sugar cane;paper; bagasse; bamboo; corn stalks; various tree portions includingsawdust, wood or bark; straw; cork; dehydrated vegetable matter(suitably dehydrated carbonhydrates such as citrus pulp, oatmeal,tapioca, rice grains, potatoes, carrots, beets, and various grainsorghams); whole ground corn cobs; or various plant portions the corncob light density pith core, the corn cob ground woody ring portion, thecorn cob coarse or fine chaff portion, cotton seed stems, flax stems,wheat stems, sunflower seed stems, soybean stems, maize stems, rye grassstems, millet stems, and various mixtures of these materials.

Optionally a dispersant for the comminuted plant material in the rangeof about 1 to about 20 pounds, preferably in the range of about 5 toabout 10 pounds, and more preferably in the range of about 7 to about 8pounds of dispersant may be utilized per pound of comminuted plantmaterial. A non-limiting example of a dispersant would be NaCl.

Preferred comminuted materials useful in the practice of the presentinvention include those derived from peanuts, wood, paper any portion ofrice seed or plant, and any portion of corn cobs.

These various materials can be comminuted to very fine particle sizes bydrying the products and using hammer mills, cutter heads, air controlmills or other comminution methods as is well known to those of skill inthe comminution art. Air classification equipment or other means can beused for separation of desired ranges of particle sizes using techniqueswell-known in the comminution art.

Any suitable size of comminuted material may be utilized in the presentinvention, along as such size produces results which are desired. Ofcourse, the particle size will be a function of diameter of the porositypassages. While the present invention will find utility for passages onthe order of microns in diameter, it will also find utility on largerpassages, for example, those with diameters greater than 1/64, 1/16 orevent ⅛ of an inch.

In most instances, the size range of the comminuted materials utilizedherein will range from below about 8 mesh (“mesh” as used herein refersto standard U.S. mesh), preferably from about −65 mesh to about −100mesh, and more preferably from about −65 mesh to about −85 mesh.Specifically preferred particle sizes for some materials are providedbelow.

Preferred mixtures of comminuted materials useful in the practice of thepresent invention include a rice fraction and peanut hulls; a ricefraction and wood fiber and/or almond hulls; a rice fraction and a corncob fraction, preferably a chaff portion; and a corn cob fraction,preferably a pith or chaff portion, a rice fraction, and at least one ofwood fiber, nut shells, paper and shredded cellophane.

Rice is commercially available in the form of rice hulls, rice tips,rice straw and rice bran, as these various parts of the rice plant areseparated commercially and are widely available from rice mills.Preferably, the size range of the rice fraction utilized herein willrange from below about 8 mesh (“mesh” as used herein refers to standardU.S. mesh), preferably from about −65 mesh to about −100 mesh, and morepreferably from about −65 mesh to about −85 mesh.

After the corn kernals are removed, corn cobs consist of four principleparts that are arranged concentrically. The central portion is a verylight density pith core, that is surrounded by a woody ring, that inturn is surrounded by a coarse chaff portion, that in turn is covered bya fine chaff portion. The coarse and fine chaff portions form thesockets for ancoring the corn kernels to the corncob. The normal methodsof grinding corncobs produce a mixture of all four parts enumeratedabove. It is possible, however, to separate the woody ring material fromthe remainder of the cob. The chaff portion of the corncob remainingafter removal of the woody ring material is known as “bees wings”. Inthe present invention, any of the pith or chaff portions (“BPC”) are thepreferred portions of the corn cob, with the chaff portions being morepreferred. A range of particle sizes of pith and chaff can be obtainedfrom comminution, but the size range smaller than about 8 mesh issuitable for this invention. Preferably, a particle size distributionranging from smaller than 8 mesh to smaller than 100 mesh is utilized.

Preferred woods for use as comminuted materials in the present inventioninclude any type of hard wood fiber, including cedar fiber, oak fiber,pecan fiber and elm fiber. Preferably the wood fiber comprises cedarfibers.

Preferred nut shells for use in the present invention include pecan,walnut, and almond. Preferably, the nut shells comprise at least one ofpecan or walnut shells.

Preferred particle sizes for the wood fibers, nut shells, paper andcellophane will generally range from about +10 mesh to −100 mesh. Anillustration of a non-limiting particle size distribution for thesematerials would include particles of +10 mesh, +20 mesh, +30 mesh, +50mesh, +60 mesh, +100 mesh, and −100 mesh.

For one of the preferred comminuted plant mixtures comprising a corn cobfraction, a rice fraction, and at least one of wood fiber, nut shells,paper and shredded cellophane, the mixture will generally comprise inthe range of about 5 to about 95 weight percent rice, in the range ofabout 5 to about 95 weight percent corncob pith or chaff, with the totalof ground wood fiber, ground nut shells, ground paper and shreddedcellophane comprising in the range of about 5 to about 95 weight percent(weight percent based on the total weight of plant material in themixture. Preferred ranges are about 20 to about 75 weight percent rice,about 5 to about 35 weight percent corncob pith or chaff, with the totalof ground wood fiber, ground nut shells, ground paper and shreddedcellophane comprising in the range of about 20 to about 75 weightpercent. More preferred ranges are about 30 to about 50 weight percentrice, about 10 to about 30 weight percent corncob pith and chaff, withthe total of ground wood fiber, ground nut shells, ground paper andshredded cellophane comprising in the range of about 25 to about 50weight percent.

As these comminuted materials are to be added to a water baseconformance fluid, a small amount of oil may optionally added to themixture. This optional oil is preferably added while the plant materialsare being mixed together. This mixing may take place in a ribbonblender, where the oil in the required amount is applied by a spray bar.The oil wets the particles and adds to their lubricity while at the sametime helping to control dust produced by the mixing operation. A varietyof oils may be utilized in the practice of the present invention inconcentrations generally ranging from about 1 percent to about 5 percentby weight based on the total weight of the mixture of comminutedmaterials, more preferably ranging from about 1 percent to about 2percent. A non-limiting example of a commercially available oil suitablefor use in the present invention includes ISOPAR V, available from ExxonCorporation.

In the method of the present invention for forming a tubing/casingannulus plug additive, the various components of polymer, crosslinkingagent and filter aid, may be mixed in any form (dry form, liquid form,or slurry form) in any suitable order utilizing mixing techniques asknown to those in the art.

Specifically, a dry tubing/casing annulus plug additive may be formed bymixing solid polymer, solid crosslinking agent and solid filter aid toform a solid (dry) tubing/casing annulus plug additive.

In the practice of the present invention, liquid tubing/casing annulusplug additive may be formed by mixing the various components in any form(dry form or liquid or slurry form) in any suitable order utilizingmixing techniques as know to those in the art. If the various componentsare mixed in dry form, this dry mixture may subsequently may becontacted with water or aqueous solution to form a liquid tubing/casingannulus plug additive.

Tubing/casing annulus plug fluids are known to those of skill in theart, and would generally be of the category of well fluid known ascompletion fluids. Generally such fluids are liquids in which a densityagent has been included to increase the density of the fluid (generallysome type of metal salt), and under certain limited circumstances mayoptionally also include a solid phase (making it more like a traditionaldrilling fluid).

In a method of treating a tubing/casing annulus plug fluid, thetubing/casing annulus plug fluid to be treated is contacted with aliquid or solid form of the tubing/casing annulus plug additive of thepresent invention. Preferably, the tubing/casing annulus plug fluid iscontacted with a dry mixture (i.e., solid form) of the tubing/casingannulus plug additive. Of course, the various components of the additive(i.e., polymer, crosslinking agent, and filter aid) may be addedindividually to the tubing/casing annulus plug fluid to be treated.

A well fluid of the present invention comprises an aqueous component,polymer, crosslinking agent, and filter aid. A modified tubing/casingannulus plug fluid comprises a traditional tubing/casing annulus plugfluid and the tubing/casing annulus plug additive or fluid of thepresent invention.

In a method of operating a well of the present invention in which a wellfluid is circulating down from the surface of the well, through thedrill string positioned in a wellbore, and out through openings in thedrill bit such that the well fluid is then circulated upwardly in theannulus between the side of the wellbore and the rotating drill string,the present invention includes circulating such a well fluid comprisingthe tubing/casing annulus plug additive. The tubing/casing annulus plugadditive can be added to the circulating fluid in liquid or solid formor of course, the individual components may be added to the circulatingfluid in liquid or solid form. Alternatively, the tubing/casing annulusplug additive may be added to the fluid prior to it being circulated.

In well operation, it is also known to define a vertically limited zoneinto which a slurry is then pumped and subsequently squeezed byapplication of pressure (either from the formation itself, or byapplication of pressure to the zone). In a method of performing a welloperation of the present invention, the tubing/casing annulus plug fluidof the present invention is pumped into a desired vertically definedzone in the well, and then “squeezed” to dewater the fluid such that aplug of the filter aid remains behind and the solution of polymer andcrosslinking agent migrates into the formation. The filter aid plugremains in place to prevent or slow down the escape of the solution backinto the well allowing time for the solution to form a gel plug. In thiswell operation, one may start with a well fluid containing the polymer,crosslinking agent and filter aid, or these various components may beintroduced to the well fluid in any combination/or of one or more inliquid or dry form, or as the additive or tubing/casing annulus plugfluid as discussed above.

The various components of the present invention may be mixed in anysuitable order utilizing mixing techniques as known to those in the art,including dry mixing of the various components prior to addition towater, or alternatively, either or both of the polymer and cross-linkingagent may be utilized as a solution. Most preferably, the variouscomponents are mixed in dry form, and then contacted with water oraqueous solution to form a tubing/casing annulus plug fluid. Thistubing/casing annulus plug fluid is then injected into the well as isknown in the art.

It is apparent that one can produce gels across a very broad range ofgelation rates and gel properties as a function of the gelationconditions. Thus, to effect an optimum plugging job according to thepresent process, the practitioner predetermines the gelation rate andproperties of the resultant gel which meet the demands of the givenwellbore and thereafter produces the gel having these predeterminedcharacteristics. The demands of the wellbore include the in situgelation conditions such as temperature, connate water properties, sizeof the treatment volume, the pressure drop and permeability of theadjoining matrix as well as the post treatment conditions such asinjection and production pressures. Analytical methods known to oneskilled in the art are used to determine these demands which providecriteria to predetermine the gelation rate and resultant gel propertiesin the manner described above and continuing hereafter.

The gelation rate is advantageously sufficiently slow to enablepreparation of the gelation solution at the surface and injection of thesolution as a uniform slug into the wellbore annulus. Too rapid agelation rate produces excessive gelation of the solution at the surfacewhich results in a solution that may be difficult, if not impossible, toinject into the annulus to be plugged due to its rheological properties.At the same time, the gelation rate must be sufficiently rapid to enablecompletion of the reaction within a reasonable period of time so thatthe well may be activated after the plugging job.

The solution may be substantially ungelled before reaching the annulus.However, at least partial gelation of the solution may be advantageousbefore the solution reaches the annulus being plugged. Partial gelationprevents the solution from penetrating permeable rock in fluidcommunication with the annulus. Substantial penetration of permeablerock by the solution and its ensuing permeability reduction may becounterproductive to the plugging of the annulus. The solutionadvantageously gels to completion in the annulus. The values of theindependent variables in the process are carefully selected to achieve agelation rate meeting these criteria.

The amount of solution injected into the wellbore is a function of thevolume of the annulus to be plugged. One skilled in the art candetermine the required amount of a gel for a given volume to be plugged.Placement of the gelation solution in the annulus may be facilitated byzone isolation means such as packers and the like.

The injection rate is a function of the gelation rate and operationalconstraints of injection pressure and pumping limits. The requiredinjection rate is fixed such that all of the solution can be practicallyinjected into the annulus before it becomes unpumpable. The gelationtime of the gel ranges from near instantaneous up to 48 hours or longer.Longer gelation times are limited by practical considerations of lostproduction when injection and production wells are shut in.

Gels having a predetermined gelation rate and resultant gel propertiesto meet the demands of a given well are produced by adjusting andsetting the surface gelation conditions as they correlate to thegelation rate and gel properties. Accordingly the gels are produced in amanner which renders them insensitive to most extreme formationconditions. The gels can be stable at formation temperatures as high as130° C. or more and at any formation pH contemplated. The gels arerelatively insensitive to the stratigraphy of the rock, metal tubularsand other materials and chemicals employed in cementing operations. Thegels can be employed in carbonate and sandstone strata andunconsolidated or consolidated strata having varying mineralogy. Oncethe gels are in place, it is extremely difficult to displace the gels byphysical or chemical means other than total destruction of thecrosslinked network. The gels may be reversible on contact with hydrogenperoxide or sodium hypochlorite, but are substantially insoluble in theformation fluids.

The process is applicable to most oil field wells having a tubing stringwithin a cased wellbore. The process is employed as a remedial treatmentprocess in wellbores having leaking tubulars to displace unwanted brinefrom the tubing/casing annulus. The process also prevents the subsequentencroachment of brine into the annulus. The process is further employedas a preventive treatment process in new or non-leaking wellbores topreclude brine from entering the annulus should tubular leakssubsequently develop.

The strength of the gel can vary from an elastic jelly-like material toa rigid rubber-like material depending upon the performance demands ofthe wellbore. The gel is designed to be sufficiently strong not to flowunder the maximum rheological stress encountered in flow conduits of thewellbore. Yet, the gel is advantageously not so strong that the tubingcannot be subsequently pulled after treatment if desired. Pulling of thetubing can be facilitated by initially coating the tubular surfaces tocontact the gel with a friction-reducing material, such as Teflon,plastic, or grease, prior to applying the process of the presentinvention.

Stronger rigid gels are generally preferred where extreme drawdownpressures are encountered during production of a well or where extremeinjection pressures are encountered during injection of fluids into awell which could cause a weak gel to fail. PA is often preferred forsuch formulations because it has a slower gelation rate than PHPA whichenables one to inject it into a volume before it sets up.

EXAMPLES

The following examples are provided merely to illustrate some but notall of the embodiments of the present invention, and are not intendedto, nor do they, limit the scope of the claims.

DE

The DE utilized in this example was that produced by Eagle PicherMinerals, Inc., and sold under the trademark CELATOM® Diatomite ET-905.As measured, the particle size distribution was:

-   -   8%+200 mesh    -   92%−200 mesh

Polymer

The polymers utilized were obtained from Ciba and a water-soluble,crosslinkable, carboxylate-containing acrylamide polymers, CIBA 254 (MWfrom 300,000 to less than 500,000) and CIBA 935 (MW from 6 to 9million).

Crosslinking Agent

The crosslinking agent was chromium acetate.

-   -   Formulations        -   Formulation No. 1            -   17.5 grams 254            -   5 grams CrIII Acetate            -   27.5 grams DE        -   Formulation No. 2            -   12 grams 254            -   3 grams CrIII Acetate            -   25 grams DE        -   Formulation No. 1            -   5 grams 935            -   3 grams 254            -   1.2 grams CrIII Acetate            -   30.8 grams DE

Filter Press Test

This test was run to simulate the dewatering of the DE in a subterraneanformation, and subsequent formation of a plug of DE and separatecrosslinked polymer.

30 ml. of plain tap water was added to a beaker and subjected to mixingat 10,000 rpm in a Hamilton Beach commercial drink mixer with a solidagitator. To this blending water was added the above formulations (threeseparate runs). The sample was allowed to blend for 5 minutes at 10,000rpm. After the 5 minutes of blending, this mixture was placed into thecylinder of a filter press in which substantial dewatering of the DEslurry occured without any pressure applied. Subsequently, 80 psi ofpressure was applied to further dewater and consolidate the DE. Finally,heat was applied to the filter press to heat the consolidated DE andliquid run off. Both the filter press cylinder and collected run off(water soluble crosslinkable polymer and crosslinking agent-no visibleDE) were placed into a 160 deg. F. water bath and allowed to crosslink.Without being limited in theory, applicant believes that residualpolymer remaining in the DE after dewatering crosslinks and serves topromote the consolidation of the DE. Once crosslinked, the collected runoff for all of the formulations promotes a rigid ringing gel.

While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be apparent to and can be readily made by thoseskilled in the art without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the scope of the claimsappended hereto be limited to the examples and descriptions set forthherein but rather that the claims be construed as encompassing all thefeatures of patentable novelty which reside in the present invention,including all features which would be treated as equivalents thereof bythose skilled in the art to which this invention pertains.

1. A method of modifying a tubing/casing annulus plug fluid comprising:(a) contacting the tubing/casing annulus plug fluid with a water solublecrosslinkable polymer, crosslinking agent, and filter aid to form amodified tubing/casing annulus plug fluid, wherein the filter aid isselected from the group consisting of diatomaceous earth, perlite, glassbeads, magnesium silicate, solid thermoplastic or thermoset polymerbeads, talc, and calcium silicate.
 2. The method of claim 1, wherein thepolymer is a carboxylate-containing polymer, and the crosslinking agentis selected from the group consisting of chromium (III) carboxylatecomplexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde,dichromates, titanium chelates, phenols, substituted phenols, ethers,aluminum citrate, and aluminates.
 3. The method of claim 2, wherein thefilter aid comprises at least one of diatomaceous earth or pearlite. 4.The method of claim 3, wherein the polymer comprises a low molecularweight polymer having a molecular weight less than 1,000,000, and a highmolecular weight polymer having a molecular weight of at least1,000,000.
 5. The method of claim 3, wherein the polymer is a watersoluble, carboxylate containing acrylamide, and the crosslinking agentis a chromium (III) carboxylate complex.
 6. The method of claim 5,wherein the filter aid is diatomaceous earth.
 7. The method of claim 5,wherein the filter aid is pearlite.
 8. The method of claim 1, whereinthe water soluble crosslinkable polymer, crosslinking agent, and filteraid, are all in solid form.
 9. A method for plugging a tubing/casingannulus formed between a casing and a tube internal to the casing in awellbore in fluid communication with a subterranean hydrocarbon-bearingformation, the method comprising: (a) providing a tubing/casing annulusplug fluid comprising water soluble crosslinkable polymer, acrosslinking agent, and a filter aid; (b) injecting the tubing/casingannulus plug fluid into the annulus; and (c) dewatering the fluid toform a filter aid plug, and to form a dewatered fluid which subsequentlycrosslinks to substantial completion in said annulus to substantiallyplug said annulus, wherein the filter aid is selected from the groupconsisting of diatomaceous earth, perlite, glass beads, magnesiumsilicate, solid thermoplastic or thermoset polymer beads, talc, andcalcium silicate.
 10. The method of claim 9, wherein the polymer is acarboxylate-containing polymer, and the crosslinking agent is selectedfrom the group consisting of chromium (III) carboxylate complexes,aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates,titanium chelates, phenols, substituted phenols, ethers, aluminumcitrate, and aluminates.
 11. The method of claim 10, wherein the filteraid comprises at least one of diatomaceous earth or pearlite.
 12. Themethod of claim 11, wherein the polymer comprises a low molecular weightpolymer having a molecular weight less than 500,000, and a highmolecular weight polymer having a molecular weight of at least 500,000.13. The method of claim 11, wherein the polymer is a water soluble,carboxylate containing acrylamide, and the crosslinking agent is achromium (III) carboxylate complex.
 14. The method of claim 13, whereinthe filter aid is diatomaceous earth.
 15. The method of claim 13,wherein the filter aid is pearlite.
 16. The method of claim 13, furthercomprising reinforcing material selected from the group consisting ofhydrophilic fibers, hydrophobic fibers, and comminuted plant material.17. A method for plugging a tubing/casing annulus formed between acasing and a tube internal to the casing in a wellbore in fluidcommunication with a subterranean hydrocarbon-bearing formation, themethod comprising: (a) providing a tubing/casing annulus plug fluidcomprising water soluble crosslinkable polymer, a crosslinking agent,and filter aid; (b) injecting the tubing/casing annulus plug fluid intothe annulus; and (c) applying pressure to dewater the fluid to form afilter aid plug, and to form a dewatered fluid which subsequentlycrosslinks to substantial completion in said annulus to substantiallyplug said annulus, wherein the filter aid is selected from the groupconsisting of diatomaceous earth, perlite, glass beads, magnesiumsilicate, solid thermoplastic or thermoset polymer beads, talc, andcalcium silicate.
 18. The method of claim 17, wherein the polymer is acarboxylate-containing polymer, and the crosslinking agent is selectedfrom the group consisting of chromium (III) carboxylate complexes,aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates,titanium chelates, phenols, substituted phenols, ethers, aluminumcitrate, and aluminates.
 19. The method of claim 18, wherein the filteraid comprises at least one of diatomaceous earth or pearlite.
 20. Themethod of claim 19, wherein the polymer comprises a low molecular weightpolymer having a molecular weight less than 500,000, and a highmolecular weight polymer having a molecular weight of at least 500,000.21. The method of claim 19, wherein the polymer is a water soluble,carboxylate containing acrylamide, and the crosslinking agent is achromium (III) carboxylate complex.
 22. The method of claim 21, whereinthe filter aid is diatomaceous earth.
 23. The method of claim 21,wherein the filter aid is pearlite.
 24. The method of claim 21, furthercomprising reinforcing material selected from the group consisting ofhydrophilic fibers, hydrophobic fibers, and comminuted plant material.25. A method of circulating a tubing/casing annulus plug fluid in awelbore penetrating a subterranean formation, comprising: (a) providinga tubing/casing annulus plug fluid comprising water or an aqueoussolution, water soluble crosslinkable polymer, a crosslinking agent, anda filter aid; (b) circulating the tubing/casing annulus plug fluid inthe wellbore wherein the filter aid is selected from the groupconsisting of diatomaceous earth, perlite, glass beads, magnesiumsilicate, solid thermoplastic or thermoset polymer beads, talc, andcalcium silicate.
 26. The method of claim 25, wherein the polymer is acarboxylate-containing polymer, and the crosslinking agent is selectedfrom the group consisting of chromium (III) carboxylate complexes,aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates,titanium chelates, phenols, substituted phenols, ethers, aluminumcitrate, and aluminates.
 27. The method of claim 26, wherein the filteraid comprises at least one of diatomaceous earth or pearlite.
 28. Themethod of claim 27, wherein the polymer comprises a low molecular weightpolymer having a molecular weight less than 500,000, and a highmolecular weight polymer having a molecular weight of at least 500,000.29. The method of claim 27, wherein the polymer is a water soluble,carboxylate containing acrylamide, and the crosslinking agent is achromium (III) carboxylate complex.
 30. The method of claim 29, whereinthe filter aid is diatomaceous earth.
 31. The method of claim 29,wherein the filter aid is pearlite.
 32. The method of claim 29, furthercomprising reinforcing material selected from the group consisting ofhydrophilic fibers, hydrophobic fibers, and comminuted plant material.33. A method of modifying a tubing/casing annulus plug fluid circulatingin a wellbore penetrating a subterranean formation, comprising: (a)introducing a water soluble crosslinkable polymer, crosslinking agent,and filter aid to the circulating tubing/casing annulus plug fluidwherein the filter aid is selected from the group consisting ofdiatomaceous earth, perlite, glass beads, magnesium silicate, solidthermoplastic or thermoset polymer beads, talc, and calcium silicate.34. The method of claim 33, wherein the polymer is acarboxylate-containing polymer, and the crosslinking agent is selectedfrom the group consisting of chromium (III) carboxylate complexes,aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates,titanium chelates, phenols, substituted phenols, ethers, aluminumcitrate, and aluminates.
 35. The method of claim 34, wherein the filteraid comprises at least one of diatomaceous earth or pearlite.
 36. Themethod of claim 35, wherein the polymer comprises a low molecular weightpolymer having a molecular weight less than 500,000, and a highmolecular weight polymer having a molecular weight of at least 500,000.37. The method of claim 35, wherein the polymer is a water soluble,carboxylate containing acrylamide, and the crosslinking agent is achromium (III) carboxylate complex.
 38. The method of claim 37, whereinthe filter aid is diatomaceous earth.
 39. The method of claim 37,wherein the filter aid is pearlite.
 40. The method of claim 33, whereinthe water soluble crosslinkable polymer, crosslinking agent, and filteraid, are all in solid form.